For example, in a retracting apparatus (including a rewinding function) for an elongated article having a belt shape or a string shape, a winding drum (sometimes called drum or spool) that retracts the elongated article rotates relative to a support unit that rotatably supports the winding drum. As for the apparatus that undergoes such relative motion, in the case where the elongated article is entirely extended or the case where the winding drum stops during retracting or rewinding, large load acts on the apparatus and the elongated article; therefore, it is preferable that an energy absorption apparatus be disposed between objects that undergo relative motion. As an example of such retracting apparatuses, a seatbelt retractor for use in a seatbelt apparatus is a representative example (refer to, for example, PTL 1 or PTL 2).
PTL 1 discloses a seatbelt retractor in which a torsion bar and a wire are disposed between a retraction drum and a ratchet gear that rotate relative to each other. According to that seatbelt retractor, energy that can occur between the retractor drum and the ratchet gear because of torsional deformation of the torsion bar and sliding deformation of the wire is able to be absorbed, and an energy absorption characteristic is able to be changed by varying the withdraw load necessary to cause the wire to undergo sliding deformation.
PTL 2 discloses a force limiter apparatus for a vehicle in which ring discs (1, 3) and an oscillation member (2) are disposed between objects that rotate relative to each other. According to that apparatus, when the oscillation member (2) rotates relative to the ring discs (1, 3), projections (5) formed on the oscillation member (2) contact projections (7, 8) formed on the ring discs (1, 3) while alternately oscillating, whereby energy that occurs between the objects that rotate relative to each other is able to be absorbed. Particularly, in this apparatus, the kinetic energy changes depending on the rotation speed of the oscillation member (2), and the energy absorption amount can be increased as the rotation speed of the oscillation member (2) increases.